I use cromfs to archive finished projects and I wanted to be able to browse them easily with Nautilus (but this script is in no way gnome-specific). I also wanted to be able to unmount them as easily because I am a clean person.

First, install cromfs (from gentoo bug #146694 and try it, it is a read-only fs with an excellent compression ratio. It is very slow at packing (similar to 7z) but since I use it for archiving, I just do it once and do not care about that. It, however, mounts the fs fast and is not memory hungry or CPU hungry anymore when browsing the archive or extracting parts of its contents. That is exactly what it has been designed for!

Then associate the cromfs extension with this script in your fav file browser. Click on the archive to mount it, click it again to unmount, the script decides which to do. The archive will be mounted in a directory with the same name as the cromfs image minus the extension.

If you prefer another type of archive (userspace or not) e.g.: cramfs, squashfs... you just need to change the MNT_CMD and maybe UMNT_CMD as you see fits; have the arguments in there too.